Data carriers, such as driving licenses, identity cards, membership cards, badges or passes, passports, discount cards, banking cards, money cards, multi-application cards, and other papers of value; and security documents such as bank notes are widely used. Because of the value and importance associated with each of these data carriers, they are often the subject of unauthorized copying and alterations, and forgeries.
To prevent one or more such activities from being carried out on these data carriers, different types of security features are used in the data carriers. One such security feature is to superimpose a pattern of guilloche lines onto an identification image.
Typically, superimposing a first image onto a second image involves merely replacing the pixels of the second image with respective pixels of the first image that are corresponding in position thereto. When using such a method to superimpose a set of black guilloche lines onto a black and white portrait type identification image during personalization may result in the guilloche lines not being visible in the darker portions of the identification image. This invisibility of the guilloche lines on the identification image is not acceptable since it does not allow post personalization modification of the identification image to be easily detected.
Such a problem is present in a known data carrier, wherein a pattern of guilloche lines is printed on a substrate. During personalization, the guilloche lines are printed before the portrait image. When printing the portrait image, a personalization system may either detect the location of guilloche lines or obtain information of the location of these guilloche lines stored in a memory of the personalization system. Portions of the portrait image that are determined to be overlapping these guilloche lines are removed from the portrait image or ignored and are not printed. Only the portions of the portrait image which do not overlap the guilloche lines are printed. The portrait image therefore does not overwrite the guilloche lines and is printed independently of the guilloche lines. It may therefore be possible that the guilloche lines are of the same shade as part of the portrait image and may thus not be visible in those parts of the portrait image.
Furthermore, the personalization method described above suffers from another disadvantage. Each of the guilloche lines may be laser printed to a thickness of about 100 microns. Current personalization systems are able to detect guilloche lines of such a thickness and to accurately laser print the portrait image so that it does not encroach on the guilloche lines. However, it is possible with some lasers to print lines that are thinner, in the range of between 10 to 20 microns. Thinner lines are advantageous because accurate detection of such lines may not be possible during forgery, making accurate forgery difficult. Unfortunately, it also makes it more difficult during personalization to accurately laser print the portrait image over the guilloche lines without the portrait image encroaching on the guilloche lines. More accurate and thus expensive equipment for laser printing is necessary.
It is therefore desirable to be able to superimpose a first image onto a second image so that the first image is visible thereon and using such an image superimposing method in a personalization method to personalize data carriers, enabling it to be less error prone compared to the prior art without compromising protection against forgery and manipulation.